Pinterest engineer Tracy Chou remembers being instantly impressed
by the professor of her Network Analysis class back
when she was at Stanford for grad school in 2009.

The class delved deep into large-scale social networks studies
—research which was still relatively new — and professor Jure
Leskovec was breaking ground.

"It was the coolest subject ever and Jure was super bad-ass,"
Chou says. "He was very young but had already written around 20
papers."

Chou loved the class (and scored an A), but after she finished
graduate school in 2010, she only ever kept in touch with
Leskovec through social media. That could have been the end of
the story.

But it isn't.

Fast-forward four years, and Chou randomly bumped into Leskovec
at a dinner party in September 2014. At that point, she had been
a software engineer at Pinterest since 2011. He had cofounded a
stealthy machine-learning ads startup ("You won't find anything
information about it," Leskovec said, when Chou asked him for its
name).

Leskovec, his cofounder Lance Riedel, and the rest of the
startup's small team had built a product graph that could map the
relationships between tens-of-millions of different products.
They were using that system to match mobile advertisers to
consumers.

Pinterest's Tracy
ChouPinterest

Chou had just joined Pinterest's ads engineering team, and the
two volleyed ideas back-and-forth for hours. When Chou left that
night, she made a mental note to talk to talk to her team about
perhaps finding some way to partner with Leskovec or share data.

"It all happened incredibly quickly," Chou says. "Everyone wanted
to move fast. We saw such talent in the team and the technology
was amazing. The opportunity was too good to pass up."

Several of Kosei's employees (there are ten total) will join
Pinterest and the companies are in the process of figuring out
how best to integrate the technology to spur the social
networking site's discovery and monetization efforts.

The acquisition comes at a crucial time for Pinterest, a $5
billion company since it raised $200 million in May. Not only has it
been significantly ramping up its amount of advertising, but it's
been trying to tackle the "discovery
problem."

Pinterest wants to fill the gap between an idea and a specific
search. It wants to help people find things they didn't know they
were looking for or when they only have the faintest glimmer
of an idea. If Pinterest can nail visual search, it can nail
search advertising, and if it can nail search advertising, it
will be
taking on a market traditionally dominated by Google's
AdWords.

Kosei's technology will help achieve both goals, by helping users
find better pins and helping advertisers reach the users they
want. Or, at least that's
the goal.